The present invention relates to magnetic disk drives, optical disk drives and other information recording and reproducing apparatus and their application systems. In particular, the invention is applicable to an information recording and reproducing apparatus which employs batteries as its power source and is operated mainly to read out information.
Recently, high density recording technology has remarkably developed and advanced in magnetic disk drives, optical disk drives and the like. Information recording and reproducing apparatus now in practical use include those which can store more than several or several ten gigabytes with media of as small as 25 to 45 mm in diameter. Making use of the compactness and large capacity, these information recording and reproducing apparatus are widely used in portable application systems including portable computers, portable music players and portable video viewers. Many of these application systems depend on either alkaline manganese and other primary batteries or Ni—Cd, Ni—MH, Li-ion and other secondary batteries as their power sources. However, these batteries have not yet reached a satisfactory level in terms of capacity (continuously dischargeable electric energy) giving the electric energy required to satisfy the demand for longer continuous operating time periods. The most direct solution for reducing the power consumed by an information recording and reproducing apparatus and its application system is to lower the maximum power consumption of each functional block by making its energy consumption more efficient. To make the energy consumption more efficient, it is necessary to, for example, make each component smaller and lighter, miniaturize the circuit, lower the operating voltage and change the principle of operation. By these methods, however, it is difficult to immediately and remarkably reduce the power consumption.
Therefore, application systems of information recording and reproducing apparatus employ such a feature that if any access has not occurred to an information recording and reproducing apparatus over a relatively long time period or if no access is likely to occur for a relatively long time period, the information recording and reproducing apparatus is forced into a low power consumption mode such as a standby mode or sleep mode. Power consumption by an information recording and reproducing apparatus in such a low power consumption mode is suppressed to about tenth of that in an active mode such as an active idle mode or read/write mode. Therefore, as the low power consumption mode period increases with respect to the active mode period, the average power consumption by the information recording and reproducing apparatus and the total average power consumption by its application system can be reduced increasingly. If the total average power consumption by the application system is reduced, it is consequently possible to make the power supply section smaller and lighter or extend the continuous operation time per battery exchange or charge.
However, when the information recording and reproducing apparatus returns to an active mode (becomes active again) from a low power consumption mode, its total power consumption greatly exceeds that in the active mode since respective functional blocks simultaneously consume power to initialize them and start mechanisms. Although the aforementioned feature can reduce the average power consumption of the system, it has posed a problem in that an operational impact is given to the information recording and reproducing apparatus and its application system when the mode returns to an active mode from a low power consumption mode. That is, even when the power supply has a current supply capacity enough to sustain the active mode, the information recording and reproducing apparatus may increase the consumption current beyond the capacity when upon reactivation. In this case, due to the output impedance of the power supply, the input power supply voltage to the information recording and reproducing apparatus may greatly fall and make the system unreliable. For example, the system may stop, go out of control and improperly issue the reset signal. Also if the power supply uses a battery, it may be judged wrongly due to the instantaneous fall of the power supply voltage that the battery is exhausted despite the amount of discharge yet lower than prescribed. In this case, the system may be stopped without being reactivated. The direct method to solve these problems is to reduce the output impedance of the power supply by enlarging the output capacity of the power supply. However, enhancing the power supply output merely to solve the problem of current supply during reactivation is remarkably disadvantageous in terms of system cost. In the case of a portable apparatus which mainly uses a battery as the power source, it is necessary to use a larger battery, which not only raises the system cost but also deteriorates the portability due to the enlarged size and increased weight of the system. Therefore, this method has not become an effective solution. In addition, when the battery is rapidly discharged to activate or reactivate the information recording and reproducing apparatus, the battery instantaneously generates heat within the battery cells due to the internal resistance. This deteriorates the energy retrieval efficiency and may degrade the cyclability of the battery, which is disadvantageous in terms of system maintenance cost.
Techniques have been disclosed as solutions for these problems. A first prior technique is disclosed in Japanese Patent Laid-open No. 2003-189676 “DISK DRIVE AND SPINDLE MOTOR CONTROL CIRCUIT”. According to the disclosure, a capacitor is charged by a counter electromotive force which occurs in the motor when the motor is stopped. When the motor is next started, the energy accumulated in the capacitor is supplied to the rotation speed control circuit in order to reduce the power supply current. A second prior technique is disclosed in Japanese Patent Laid-open No. 6-119708 “OPTICAL DISK DRIVE AND ITS APPLICATION DEVICE”. According to the disclosure, the current supplied to the spindle motor is limited when the power consumption increases to peaks, namely when the spindle motor is restarted and when the rotation speed is changed from a steady speed. A third prior technique is disclosed in Japanese Patent Laid-open No. 2003-173638 “DISK STORAGE DEVICE AND MOTOR CONTROLLING METHOD”. According to the disclosure, if it is detected by the CPU via the current sensor that the current spent by the spindle motor of the disk storage device is larger than a predefined value when the spindle motor is started, the current supplied to the voice coil motor is limited by the CPU to within a predefined maximum value in order to reduce the current supplied to start the disk storage device. A fourth prior technique is disclosed in Japanese Patent Laid-open No. 2000-323219 “DISK STORAGE DEVICE AND SPINDLE START CONTROL METHOD USING FOR THE SAME, AND RECORDING MEDIUM ON WHICH THE CONTROL PROGRAM IS RECORDED”. According to the disclosure, the microprocessor always monitors the current consumed by drives in the disk array. If the consumed current is detected increasing beyond a threshold while a spindle is being started, starting the spindle is temporally canceled so that the current consumed by the physical disks is controlled to within the threshold. A fifth prior technique is disclosed in Japanese Patent Laid-open No. 1998-69702 “VOLTAGE ABNORMALITY DETECTING CIRCUIT OF MAGNETIC DISK DRIVE”. According to the disclosure, a voltage abnormality detecting circuit compares threshold voltage Vth with power supply voltage Vcc supplied to the magnetic disk drive. If the power supply voltage Vcc is below the threshold voltage Vth, the voltage abnormality detecting circuit outputs an abnormality signal to the main control unit in order to prevent the device from destructing data and malfunctioning. A sixth prior technique is disclosed in Japanese Patent Laid-open No. 2003-242673 “OPTICAL DISK RECORDING AND REPRODUCING APPARATUS AND METHOD”. According to the disclosure, there is provided means for monitoring the power supply voltage to the recording circuit. If the voltage is below a preset value during recording, the recording is halted or done intermittently. Continuous recording is not done until the voltage recovers in order to prevent wrong data recording.